Beamforming is a signal processing technique used in sensor arrays, for example arrays of microphones, for directional signal reception and appropriate signal processing of the received acoustical signals. Beamforming allows an assembly of microphones receiving acoustical signals to have the resulting electrical signals selectively processed, for example, treating acoustical information from one source differently than acoustical information from a different source. In contrast to omni-directional microphone assemblies which receive and process sounds uniformly regardless of source or direction, beamforming allows signals arriving from different locations to be treated differently before transmission or amplification. Beamforming allows detection of particular signals of interest by use of special filtering and interference rejection.
One potential application of beamforming microphones is in conference telephony. In conference telephony individuals may be arrayed about a room at different locations and distances from a conference telephone. The voices of some individuals may reach the microphone directly, while voices from other individuals further from the microphone may reach the microphone directly and via multiple other paths, such as by reflections off walls or windows in the room. In addition, there may be background noise originating from sources outside the room. With the use of advanced signal processing techniques, individual voices within the room may be selected and selectively processed or amplified before transmission to other parties participating in the telephone call. Background noises may be suppressed, and the relative volumes of voices equalized before transmission. A more detailed discussion of beamforming is in “A Primer on Digital Beamforming,” T. Haynes, Spectrum Signal Processing, Mar. 26, 1988 (www.spectrumsignal.com).
One disadvantage of conventional beamforming microphone arrays is their size. Typically such arrays require a relatively large footprint, often about a foot square, as typified by conventional conference room telephones. A further disadvantage of conventional beamforming microphone arrays has been the cost. Conventional conference telephones cost hundreds of dollars, precluding their use in many applications where they would be otherwise suitable. Accordingly, there is a need for a compact, low-cost, beamforming microphone array, for example as might be used with a conventional desk or office telephone.